<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        p{color: yellow}
        p span{color: green}
        /*b下面所有span的第一个*/
        b span:nth-child(1){
            color: red;
        }

        #s1,#s2{
            color: blue;
        }


        span.m1{
            color: coral;
        }
    </style>

</head>
<body>
    <!--<span>行级，无任何效果的标签
        <div> 块级，无任何效果的标签
    -->

    <p>
        <span>test</span>
        <b>
            hello
            <span>world</span>
            <span id="s1">xxxxx</span>
            <span id="s2">xxxxx</span>
            <span class="m1">xxxxx</span>
            <p class="m1">xxxx</p>
        </b>
    </p>


</body>
</html>









